1. Field of the Invention
This invention relates to an organic electro luminescence display device, and more particularly to an organic electro luminescence display device that is adaptive for improving luminous brightness and reducing power consumption, and a fabricating method thereof.
2. Description of the Related Art
Recently, there have been developed a variety of flat panel display devices that can reduce their weight and size, which are a disadvantage of a cathode ray tube CRT. The flat panel display device includes a liquid crystal display LCD, a field emission display FED, a plasma display panel PDP and an electro luminescence EL display device. Particularly, the EL display device has electrodes stuck to both of the sides of an organic light emitting layer basically composed of a hole transport layer, a light emitting layer and an electron transport layer, and becomes the center of attention as a next generation flat panel display device because of its characteristics such as wide viewing angle, high aperture ratio and high chromaticity.
The EL display device is largely divided into an inorganic EL display device and an organic EL display device in accordance with a material used. In the organic EL display device, electrons and holes form a pair and then become extinct to emit light if electric charges are injected into an organic EL layer which is formed between a hole injection electrode and an electron injection electrode, thus there is an advantage in that it can be driven at a lower voltage than the inorganic EL display device. Further, the organic EL display device can drive at a low voltage of not greater than 10V in comparison with the PDP or the inorganic ELD as well as forming the device on a flexible transparent substrate like plastics, and its power consumption is relative low and its color impression is excellent.
FIG. 1 is a perspective view representing a related art organic EL display device, and FIG. 2 is a sectional diagram representing the organic EL display device shown in FIG. 1, taken along the line “I-I′”.
The organic EL display device shown in FIGS. 1 and 2 has an anode electrode 4 and a cathode electrode formed in a direction of crossing each other on a substrate 2.
A plurality of anode electrodes 4 is formed to be separate from one another with a designated distance therebetween. An insulating film 6 having a hollow part for each EL cell (p) area is formed on the substrate 2 where the anode electrode 4 is formed. A barrier rib 8 is located on the insulating film 6, wherein the barrier rib separates an organic light emitting layer 10 and the cathode electrode 12 which are to be formed on the insulating film 6. The barrier rib 8 is formed in a direction of traversing the anode electrode 4 and has a reverse taper structure that an upper part has a wider width than a lower part. The organic light emitting layer 10 and the cathode electrode 12 composed of an organic compound are sequentially deposited on the whole surface of the insulating film where the barrier rib 8 is formed. The organic light emitting layer 10 is formed by depositing a hole related layer 10A inclusive of a hole injection layer and a hole transport layer; a light emitting layer 10C to realize color; and an electron related layer 10E inclusive of an electron transport layer and an electron injection layer.
In the organic EL display device, if a voltage is applied to the anode electrode 4 and the cathode electrode 12, the electron generated at the cathode electrode 12 moves to the light emitting layer 10C through the electron related layer 10E. Further, the holes generated at the anode electrode 4 moves to the light emitting layer 10C through the hole related layer 10A. Accordingly, in the light emitting layer 10C, the electron and the hole supplied from the electron related layer 10E and the hole related layer 10A are recombined to form an exiton, and the exiton is excited again to a ground state, thus a light of a fixed energy is emitted to the outside through the anode electrode 4.
The organic EL display device with such a configuration has the incident light from the outside almost completely transmitted through the anode electrode 4 and the organic light emitting layer 10. As a result, when the light is not emitted from the organic light emitting layer 10, an external light 40 which is incident from the surface of the substrate 2 is transmitted through the organic light emitting layer 10 and the anode electrode 4 of a transparent conductive material, and it is reflected by the cathode electrode 12 of a metal electrode, as shown in FIG. 3A. Accordingly, there is a problem in that the contrast ratio is deteriorated. In order to solve the problem, as shown in FIG. 3B, a reflection protective film 30 is used. The reflection protective film 30 is stuck to the substrate 2 of the organic EL display device to intercept the external light 40 from being emitted out of the organic EL display device by being reflected after the external light 40 is irradiated from the outside. Herein, the reflection protective film 30 includes a polarizer 30A which transmits a specific linear polarized light out of the external light 40 and intercepts the other polarization component, and a λ/4 phase difference plate 30B for converting the linear polarized light into a circular polarized light.
However, the contrast ratio can be improved if such a polarizer 30A is used, but the transmittance cannot be over 50% due to the optical characteristics of the polarizer 30A in case that a polarization ratio is not less than 99%, thus a brightness loss of not less than 50% is generated in the organic EL display panel. Accordingly, there arises a problem that the power consumption should be increased to get a desired brightness in the organic EL display device.